Communication systems are known to comprise a plurality of communication units, a limited number of communication resources (channels), an operator station, a communication resource controller, and a plurality of broadcast units. An operator, via the operator station, may select many communication units as destinations for a paging message. After selecting the desired communication units, the operator station transmits the message to all of the selected communication units via the plurality of broadcast units. Typically, there are two ways to do this: sequentially or simultaneously.
In a system that transmits sequentially, the message or paging message is sequentially sent to each communication unit. Obviously, this is an inefficient method when a large number of communication units are selected to receive a message requiring several seconds to transmit. In a simultaneous system, the message is transmitted via multiple broadcast units at the same time. This method can greatly improve the efficiency of transmitting a message to multiple communication units. However, a shortcoming of the simultaneous method is that conflicts can arise which prevent the transmission of the paging message to two or more communication units at the same time.
In systems that transmit simultaneously, a conflict occurs when paging messages are required on two different channels of a multi-channel broadcast unit. Also, paging messages cannot be simultaneously transmitted via channels which are cross-busied in the system. Cross-busied channels are channels known to interfere with one another, thus severely degrading their performance. In most simultaneous paging systems experiencing these limitations, the operator is not allowed to select communication units located in coverage areas of certain broadcast units that are known to create conflicts. To transmit a paging message to a large number of potentially conflicting communication units could take substantially longer, thus nullifying the advantage of simultaneous systems. This is a particularly crucial problem when time is in short supply, as might be the case when attempting to notify members of a volunteer fire department of an ongoing emergency.
Simulcast communication systems eliminate the problems of contention described above. Such systems typically provide single-channel coverage, thus eliminating contention, over very large geographical regions. Simulcast systems are useful when multiple communication units can be located anywhere within a large coverage area. However, such systems are expensive and are not very cost-effective when communication units are restricted to a relatively small coverage area, as would be the case for a paging system.
Therefore, a need exists for a method which allows the selection and efficient processing of conflicting communication units in a simultaneous paging system.